Optical fiber alignment method

ABSTRACT

A bundle (12) of optical fibers (13) is fixed in a matrix array by apertures in a guiding plate (14) and a securing plate (15). The apertures (18) in the guiding plate are larger than those in the securing plate and the securing plate apertures (17) are funnel-shaped to aid in insertion of the fibers. Each row of optical fibers may be inserted simultaneously by mounting the row on a uniquely designed vacuum holder (26).

Technical Field

This invention relates to optical fiber devices and, more particularly,to methods for permanently arranging the ends of optical fibers in adesired configuration.

BACKGROUND OF THE INVENTION

One of the major advances in communications in recent years has been theincreased use of optical fiber systems for carrying very largequantities of information with low distortion and low cost over greatdistances. Optical systems are also promising for such purposes ascomputing and switching because of the inherently high speeds at whichthey can be operated. For these reasons, considerable work has beenexpended to develop convenient techniques for operating directly ontransmitting information-carrying light to produce various devicefunctions, that is, without converting such light to electrical energyprior to such operations. The utilizing of such devices will depend to agreat extent on the efficiency and facility with which they can be made.

Optical fibers typically comprise a core of relatively high refractiveindex glass having a diameter of five microns surrounded by lowrefractive index glass having a diameter of one hundred twenty-fivemicrons. The paper, "All-Optical Implementation of a 3-D CrossoverSwitching Network," by T. J. Cloonan et al., IEEE Photonics TechnologyLetters, Vol. 2, No. 6, June 1990, pp. 438-440, describes a free-spacephotonics switch which takes light from the end of a bundle of opticalfibers, operates on the light so as to perform desired switchingfunctions, and then projects the light into the end of a second array ofoptical fibers. The optical fiber ends of each bundle form a matrixconfiguration which must be accurately registered with the otherapparatus. Because the size of each fiber, especially the core, is sosmall, it is important that the ends of each optical fiber bundle bepositioned with a great deal of accuracy; fixing the ends of an opticfiber bundle in a desired matrix configuration with the precision neededfor such functions as free-space photonics switching is difficult andpainstaking.

Because of their importance both to communications and to high-speedcomputing, there has been a long-felt need in the industry fortechniques that can be used to arrange the ends of optical fibers in adesired configuration, that are relatively inexpensive, that do notrequire a great deal of operator skill, and that are dependably accurateto within micron or sub-micron dimensions.

SUMMARY OF THE INVENTION

Optical fibers are arranged with their ends forming a matrix array bymaking in a planar securing plate an array of apertures corresponding tothe matrix array, and making a similar arrangement of apertures in aplanar guiding plate. The end of each optical fiber is then directedfirst through an aperture in the guiding plate and then through afunnel-shaped aperture in the securing plate. The guiding plateapertures are made sufficiently large so that the fibers can easily beinserted into them and, thereafter, each fiber is directed by the funnelshape of the securing plate through an opening sufficiently small tohold the fiber in a precise spatial relationship with respect to theother fibers. After the fibers have been positioned in the matrix arrayof apertures in the securing plate, they are filled with epoxy to make apermanent fixture, and the protruding ends of the fiber are ground to beflush with the securing plate. Thereafter, the precisely configured endsof the matrix array of optical fibers may be used, for example, as partof a free-space photonics switching system.

In accordance with one feature of the invention, a vacuum holder isprovided for holding a row of parallel optical fibers by a vacuum suchthat the optical fiber ends protrude from the holder. The optical fibersheld by the vacuum holder are then inserted into a row of apertures ofthe guiding member and then into a corresponding row of apertures in thesecuring member. During the insertion, light may be projected throughthe fibers and monitored by a television camera to align the fibers andto assure that none of the fibers have been broken and that they haveall been appropriately inserted into the securing member. The vacuum isthen released so that the vacuum holder can be removed and another rowof optical fibers inserted into it. In this manner, successive rows areformed until the entire matrix array has been completed, at which timeall of the fibers are filled with epoxy to form a permanent structure.The optical fibers may initially protrude through the securing memberand, after permanent bonding, they are around such that all of the endsof the matrix array lie on a common plane.

Both the securing member and the guiding member may be made of amaterial such as glass or ceramic in which the apertures are made byetching so as to develop the preferred shape for guiding the fibers witha minimum of stress. The securing member apertures, for example, arepreferably etched from one side of the member to give them funnelshapes. If greater positioning accuracy is required, the securing membermay be made of silicon with the apertures being formed by masking andetching along crystallographic planes. The apertures may be madesufficiently small that the fibers cannot initially protrude throughthem. Then, after insertion of all of the fibers into the securingmember apertures, the side of the securing member opposite the guidingmember may be polished until the fiber ends are exposed. The polishingmay continue until the filter ends have likewise been polished therebyto make them coplanar. The technique also can facilitate alignment of alens array to be used with the fiber matrix array.

These and other objects, features and advantages of the invention willbe better understood from a consideration of the following detaileddescription taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic sectional view of an optical fiber array that hasbeen fabricated in accordance with an illustrative embodiment of theinvention.

FIG. 2 is a schematic illustration of the securing plate of theapparatus of FIG. 1;

FIG. 3 is a sectional schematic view of part of the securing plate andguiding plate of the apparatus of FIG. 1;

FIG. 4 is a view of a vacuum holder that may be used in assembling theapparatus of FIG. 1;

FIG. 5 is a schematic view showing how the vacuum holder of FIG. 5 maybe used for inserting fibers into the apparatus of FIGS. 1 and 3;

FIG. 6 is a schematic view showing a clamping arrangement for opticalfiber ribbons that can be used in assembling the apparatus of FIG. 1;

FIG. 7 is a schematic view of part of a securing member and guidingmember that may be used in the apparatus of FIG. 1;

FIG. 8 is a schematic view of part of an optical fiber array fabricatedin accordance with another embodiment of the invention; and

FIG. 9 is a view of the guiding plate and securing plate apertures ofthe apparatus of FIG. 8;

DETAILED DESCRIPTION

The drawings are not necessarily to scale and certain parts of them havebeen simplified to aid in clarity of exposition. Referring now to FIG.1, there is shown apparatus 10 made in according with one embodiment ofthe invention so as to define a matrix array 11 of optical fiber ends.The apparatus comprises an optical fiber bundle 12 made up of aplurality of optical fiber ribbons, each ribbon comprising a row ofoptical fibers 13 held together by plastic coating. The plastic coatingis removed from the ends of individual optic fibers 13 so that the endscan extend through a guiding plate 14 and a securing plate 15.

The securing plate 15 is shown in FIG. , and it comprises a matrix arrayof apertures 17, each designed to contain one optic fiber. FIG. 3 is anenlarged sectional view of part of the guiding plate 14 and securingplate 15, and it illustrates how each optic fiber 13 extends throughboth an aperture 18 of the guiding member as well as an aperture 17 ofthe securing member 15. The guiding plate and securing plate are alignedsuch that the aperture arrays are in substantial axial alignment and theplates are spaced conveniently by a plurality of spherical members 19.

Referring again to FIG. 1, the optic fibers 13 are permanently held inplace by an epoxy 20 which bonds the separated optic fibers together andalso to the guiding member 14 and securing member 15. The epoxy iscontained by a cylindrical metal member 21 and a pair of plastic bodymembers 22 and 23. A coil 24 provides strain relief to the optic fibersbundle 12. After assembly, the apparatus 10 holds the ends of theoptical fibers 13 in a plane which constitutes a matrix array having theconfiguration of matrix array 17 of FIG. 2. Such apparatus can be usedas part of the free-space photonic switch described in theaforementioned T. J. Cloonan et al. publication.

Referring again to FIG. 3, the guiding plate 14 assists in the assemblyof the matrix array of fibers as well as constituting part of thefinished product. Each of the apertures 18 has a generally largerdiameter than the diameters 17 of the securing plate 15 and thereforefiber insertion in an aperture 18 constitutes a gross alignment of thefiber with a corresponding aperture 17. The apertures 17, in turn, areeach funnel shaped so that, when a fiber is inserted into it, it isguided to its proper spatial position in the matrix configuration. Afterassembly and bonding with epoxy, the guiding plate 14 and securing plate15 both provide mechanical support to the fiber array and make thedevice 10 quite robust.

FIGS. 4, 5, and 6 illustrate how, in accordance with the invention, anentire row of optic fibers can be simultaneously mounted in the guidingand securing plates 14 and 15. Referring to FIG. 4, a vacuum holder 26is formed comprising a row of grooves 27 for supporting a row of opticfibers 13 shown in section. Each of the grooves 27 communicates with acavity 28 and each of the cavities 28 communicates with a channel 29that extends along the vacuum holder 26. The optic fibers 13 are held inthe grooves by a vacuum applied to the channel 29 by vacuum apparatus31.

As shown schematically in FIG. 5, the optical fibers 13 are held in theholder 26 such that the ends protrude over one edge. The holder 26 mayrest on a vertical stage (not shown) while guiding plate 14 and securingplate 15 are mounted on metal member 21 which is claimed to an x-y table(not shown). Light from a source 32 is directed into the optic fibers 13and is observed by a closed circuit TV camera 33. The operator views amagnified image of the fiber ends on a TV display (not shown) andadjusts the x-y table to align the apertures in plates 14 and 15 withthe row of optical fibers. When the fibers are appropriately alignedwith the apertures, the operator operates the vertical stage to move thevacuum holder in the direction of the arrow so as to insert the ends offibers 13 through apertures 18 and 17 of guiding plate 14 and securingplate 15, respectively. After a row of optical fibers has been insertedas shown, the optical fibers are held in place by a clamp and the vacuumsource 31 is switched to remove the vacuum. Holder 26 is then moved withrespect to plates 14 and 15 to a position for receiving another row ofoptical fibers. The next row of optical fibers is inserted in the vacuumholder, the vacuum is reapplied, and the next row of fibers is insertedthrough apertures 18 and 17. This procedure is repeated until the entirematrix array of fiber ends has been mounted.

Referring to FIG. 6, the optical fibers 13 may be part of an opticalfiber ribbon 35, which, as is known, comprises a row of optical fibersheld together by a plastic coating. The plastic ribbons may be held by apair of clamps shown schematically at 37 and 38. After the fibers ofeach successive ribbon have been inserted through guiding plate 14 andsecuring plate 15, the ribbon may then be clamped to ribbon 35 bysuccessively clamping it first to one of the clamps 37, 38 and then toanother. By using two clamps, successive ribbons can be added to anarray of ribbons without distributing the array of ribbons previouslymounted. The entire succession of ribbons may constitute the opticalfiber bundle 12 of FIG. 1. After the insertion steps, optical fiber ends39 may protrude a significant distance beyond the securing plate 15, asshown. When the assembly is filled with epoxy and the structure shown inFIG. 1 is assembled, the ends 39 may likewise be bonded together withepoxy, and thereafter they can be ground off to be flush with the planarsurface of securing member 15. The epoxy bond maintains the relativepositions of the ends 39 during the polishing and reduces the chances ofspurious breaking or cracking of the fibers by providing structuralreinforcement.

In one prototype construction of the apparatus 10 of FIG. 1, the matrixarray comprised eighteen rows, each having thirty-six optical fibers,Referring to FIG. 7, the diameter a of each optical fiber 13 may be onehundred twenty-five microns, which is the dimension of commerciallyavailable fibers. The center-to-center spacing b of successive fibersmay be two hundred sixty-two microns. Both the guiding plate 14 and thesecuring plate 15 may be made of Fotoform (TM), a glass plate materialavailable from the Corning Glass Works of Corning, New York. Apertures18 in the guiding plate 14 may be made by photolithographic masking andetching from opposite sides of the plate. Etching from both surfacesinwardly leaves each aperture with an hourglass configuration, typicallyhaving a large diameter c of two hundred microns and a small diameter dat the center of guiding plate 14 of approximately one hundredthirty-five microns. Guiding plate 14 may have a thickness of fortymils, and securing member 15 a thickness of thirty mils (seven hundredfifty microns). The securing pate 15 is preferably etched only from itsupper surface so as to give a pronounced funnel shape to apertures 17.The upper surface of each aperture may have a diameter e of one hundredseventy-eight to one hundred eighty-two microns and a lower surfacediameter f of one hundred twenty-seven to one hundred thirty microns.

It an be seen that apertures 18 are generally large than apertures 17since their principal function is to guide the fibers 13 to be alignedwith apertures 17, and the larger the aperture, the easier is theinitial insertion of the fibers. Apertures 18 should not be so largethat they do not constitute a reliable alignment with apertures 17.Apertures 17 should preferably have a pronounced funnel configuration topermit easy insertion in the upper surface while having a sufficientlysmall diameter at the lower surface to constrain the position of thefiber tips in the matrix configuration. The separation g of the twoplates is not critical and may, for example, be two hundred fiftymicrons. Referring to FIG. 3, the use of several glass spheres 19mounted in apertures in the two plates as shown is a convenient methodfor obtaining a predictable spacing, since the apertures and glassspheres can easily be made with a great deal of precision anduniformity.

Referring again to FIG. 4, it is important to make the vacuum holder 26sufficiently precise that it holds fibers 13 in a common plane forsimultaneous insertion into the apertures. Cavities 28 and channel 29can be formed in steel by electron discharge machining, which involvesthe formulation of an electronic discharge by a wire that then cutsthrough the steel in a manner similar to that of a jig-saw. Electrondischarge and other forming methods that may be used are matters thatare well understood in the art and therefore have not been described indetail. The total thickness of a holder 26 that was made was sixteenmils.

Referring to FIGS. 8 and 9, there is shown another embodiment of theinvention which may be used if the alignment tolerances are even morecritical than those of the embodiment of FIG. 1. The main difference isthat the securing member 15 is made of silicon and the apertures 17 aremade by etching from the upper surface of the silicon securing member.The silicon securing member 15 is conventional <100> silicon whichinherently etches along crystallographic plates at an angle of 54.7degrees with respect to the horizontal. FIG. 9 is a top view, lookingthrough guiding plate 14 to the apertures 17 in the securing plate 15.The apertures are defined by trapezoidal side walls with rectangularopenings at the bottom, as shown. It is known from the siliconmicro-machining art that such apertures can be made with sub-micronprecision using standard photolithographic mask and etch techniques. Asa consequence, the fibers 13, when abutted at their ends against thesides of the apertures 17 as shown in FIG. 8, will necessarily beextremely precisely located. That is, there is a complete restraint ofmovement of the end of each optical fiber in any horizontal direction.

After insertion, the optic fibers 13 can be fixed by epoxy, as describedbefore. The apparatus of FIG. 8 may then be used as shown with the lightbeing emitted from the bottom of each aperture 17. Alternatively,silicon securing member 15 may have its bottom surface polished tobecome flush with the ends of fibers 13. The fiber ends may be polishedalong with the securing members 15 to insure coplanarity of the endsurfaces of the fibers.

In embodiments that were made, the guiding member 14 was one millimeterthick and was made of a ceramic version of Fotoform (TM) material. Theeight by eight array was positioned with great precision by virtue ofthe silicon securing means. The silicon securing member was five hundredeight microns thick, which was too thick to make a complete penetrationby the etched apertures. Rather, cavities having the characteristic 54.7degree slope were etched that were one hundred forty-one microns deepand two hundred microns across at the upper surface. After the opticalfibers were inserted, the wafer was polished sufficiently on the sideopposite the cavities to reach the cavities and to polish slightly theends of the fibers which were positioned with precise center-to-centerspacing in the matrix. It should be noted that terms such as "aperture"and "diameter" as used herein are intended to apply to non-circular aswell as circular openings. Likewise, the optical fiber need notnecessarily be of a cylindrical shape.

The various embodiments that have been described are intended to bemerely illustrative of the different ways in which the invention can beused. The guiding means and the securing means can be made of any ofvarious materials other than glass, ceramic and silicon that have beendescribed, including molded polymer. Etching the guiding means fromopposite sides is advantageous, but not essential, and the apertures canbe made in various other ways such as drilling. The invention may beused for arranging optical fiber ends in configurations other than amatrix configuration. Wherever the relative positions of the ends ofoptical fibers are important, the invention may be advantageous. Amatrix array of lenses having a configuration corresponding to that ofthe ends of the fibers may be used to collimate and/or direct the outputbeam or to focus incoming lightwave information. Various otherembodiments and modifications may be made by those skilled in the artwithout departing from the spirit and scope of the invention.

We claim:
 1. A method for making a device comprising an array of opticfiber ends having a desired configuration, said method comprising thesteps of:forming in a planar securing member a first array of firstapertures, said first array having a configuration corresponding to saiddesired configuration; forming in a planar guiding member a second arrayof second apertures, said second array having a configurationcorresponding to said desired configuration; the largest diameter ofeach of the second apertures being at least as large as the largestdiameter of the first apertures and larger than the diameter of theoptical fibers; aligning the first and second members along a commonaxis such that the first and second aperture arrays thereof are insubstantially axial alignment; inserting each optical fiber end firstthrough a second aperture of the guiding member and thence into acorresponding first aperture of the securing member; and permanentlybonding the optical fiber ends to the guiding and securing members. 2.The method of claim 1 wherein:the desired configuration is a matrixarray comprising a plurality of rows and columns of optical fiber ends;and the inserting step comprises the steps of (a) providing a vacuumholder for holding a row of parallel optical fibers by a vacuum suchthat the ends thereof protruded from the holder, (b) inserting a row ofoptical fibers in the vacuum holder such that they are held by a vacuum,(c) inserting the protruding ends of the optical fibers into a row ofsecond apertures and thence into a row of first apertures, (d) releasingthe vacuum, and (e) repeating the above-mentioned insertion steps (b)through (d) until the entire matrix has been inserted into the guidingand securing planar members.
 3. The method of claim 1 wherein:thelargest diameter of each of the second apertures is larger than thelargest diameter of the first apertures; and each of the first apertureshas a larger diameter on the side of the planar securing member facingthe guiding member than on the opposite side of the securing member. 4.The method of claim 3 wherein:the first apertures initially do notextend entirely through the first planar member; and, after insertion ofthe optical fibers into the first apertures, the side of the planarsecuring member most remote from the guiding member is polishedsufficiently to expose the ends of the optical fibers extending throughthe first apertures.
 5. The method of claim 4 wherein:the securingmember is made of a material selected from the group consisting ofglass, ceramic and silicon; and the first apertures are made by maskingand etching on the side of the securing member facing the guidingmember.
 6. The method of claim 5 wherein:the guiding member is made of amaterial selected from the group consisting of glass, ceramic andsilicon; and the diameter of each second aperture at the surface of theguiding member into which the optical fibers are first inserted islarger than the diameter of such apertures at the interior of theguiding member, the smallest diameter of each second aperture beingsufficiently larger than the diameter of each optical fiber to permitthe easy insertion of each optical fiber through each second aperture.7. The method of claim 2 wherein:the inserting step further comprisesthe steps of directing light into each optical fiber of the row ofoptical fibers at the end of the fiber opposite its protruding end andaligning the first and second apertures with respect to the row ofparallel optical fibers by moving the first and second apertures withrespect to the row until light from the fibers can be observed throughthe second and first apertures, and thereafter inserting the row offibers through the second and first apertures.
 8. The method of claim 2wherein:each row of optical fibers is part of a single optical fiberribbon; the portions of the optical fibers that are inserted in thevacuum holder are separated from the ribbon, and portions of the opticalfibers remote from the protruding ends are maintained as part of theribbon; and, as successive rows are inserted into the second and firstapertures, successive ribbons are clamped together to form an opticalfiber bundle.